This invention relates to image processing techniques for smoothly shading objects and/or regions in an image. Conventional image processing computer applications provide a number of image processing techniques. Commercially available applications such as Photoshop® and Illustrator®, available from Adobe Systems Incorporated, of San Jose, Calif., implement gradient fill techniques for providing smooth color transitions along a vector from one color to another within a selected region or object in an image. Thus, a gradient fill can be considered a graduated blend or transition between two or more colors (or tints or shades of a color).
Known gradient fill techniques can be divided into the following categories. First, in linear or axial gradients color varies between specified boundary colors along a line between starting and ending coordinates (called the gradient axis), forming a series of isochromal lines (lines of the same color in the transition) extending infinitely (at least within the bounds of the object or region to be filled) in directions perpendicular to the gradient axis. In a radial gradient, by contrast, color varies along the radial direction extending out from the origin (typically, the object's center), forming a series of concentric circles with each point on a given circle sharing the same color in the transition. Some applications provide a variant of the radial gradient known as a diamond gradient, in which color varies radially between concentric squares or diamonds. Finally, in an angular gradient, color varies along the angular direction around the origin, with all points on a given ray extending out from the origin sharing the same color in the transition.
In general, these conventional techniques apply gradient fills within a bounding box of the object or region to be filled. They do not, however, provide a means for using the geometry of the selected region or object to guide the application of gradient fills.